1. Field of the Invention
The present invention relates to a semiconductor container for carrying wafers/masks and more particularly, to an airtight semiconductor transferring container, which uses an elastically deformable inner lining shell and an elastically deformable packing member to keep the inside holding space in an airtight status.
2. Description of the Related Art
IC (Integrated Circuit) is one of the most important elements that construct the so-called “third wave revolution” or “information revolution”. Computer, mobile phone, Internet, and LCD are important inventions of this digital era that greatly influence the living of human beings. Because IC chip has a wide application, it is used in a variety of electronic consumer products including computer and mobile phone. Following fast development of semiconductor technology, electronic products are designed to meet the requirements of modern electronic features such as light, thin, short, small, high speed, high frequency, high performance, and high precision. Heavy market demand for electronic products having modern electronic features promotes development of semiconductor technology towards this market trend. In consequence, investment in semiconductor industry keeps increasing in recent years. Every manufacturer is trying hard to create new technology in order to take the leading place in the market so as to enjoy huge commercial profit from the market. In order to survive from severe market competition, it is important to reduce the cost and improve the efficiency in this semiconductor field.
IC fabrication is an application of photolithography. This technique is to have an electronic circuit pattern on a mask reticle be projected onto a wafer by light. After developing and baking, a contracted circuit pattern is formed on the wafer. The water thus obtained is then processed through other posterior procedures such as wafer saw, die attach, wire bond, molding . . . and etc. Therefore, reducing line width should be achieved by improving photolithographic process. A relatively smaller line-width CD value means a relative bigger number of transistors in a unit area, and the IC will have a relative stronger function, lower power consumption and lower cost. For example, when improved the manufacturing process of a 128 MB DRAM from 0.25 μm to 0.13 μm, the productivity for 8 inches wafer will be increased by 4 times, or the number of dies will not be significantly reduced when improved the production to 256 MB DRAM. This is the. Moore's law that is the observation made in 1965 by Intel co-founder Gordon Moore that each new memory integrated circuit contained roughly twice as much capacity as its predecessor, and each chip was released within 18-24 months of the previous chip.
Due to Moore's law, the successability of technical improvement toward smaller line width CD value is determined subject to photolithographic techniques, and scanner is the key implement. Currently, 248 nm deep-UV is intensively used for 0.11 μm photolithography. However, due to wavelength's sake, it is not possible to have the downward going line be in the way like 90 nm˜65 nm. Further, the use of 248 nm deep-UV for 0.11 μm lithography requires the so-called PSM (phase shift mask) reticle, which is made of molybdenum (MO) that is about 2˜3 times over the price of chromium (Cr). In order to obtain a relatively smaller line width, the wavelength of the exposure machine should be relatively shorter. Therefore, 248 nm deep-ultraviolet light is intensively used to substitute for 365 nm ultraviolet. Recently, there are manufacturers studying the use of 193 nm deep-ultraviolet photoresist and light source of ultra short wave (Argon fluoride excimer laser to generate 193 nm deep-ultraviolet light) to improve lithographic process to the stage of 0.13 μm˜65 nm.
However, current semiconductor manufacturers commonly use SMIF system provided by Hewlett-packard for storing and transporting wafers/masks, i.e., the so-called enclosed transferring container. SMIF system is designed to reduce particle flux in storage and transport of semiconductor products during a semiconductor manufacturing process. This objective is achievable by: keeping the air proximity to the wafer or mask from change relative to the wafer or mask during storage and transport so as to prevent passing of particles from the surroundings into the air proximity to the wafer or mask. SMIF system uses a small amount of particle-free air to provide a clean environment for the object where the movement and flowing direction of the air and pollutant are well controlled. This measure greatly reduces the cost for clean room.
Before using 193 nm deep-UV to run a lithographic process, as shown in FIG. 1, the photomask A and the pellicle B are stored in an enclosed storage container (semiconductor transferring container) D. When in use, the photomask A and the pellicle B are taken out of the enclosed storage container D and put in a mini-environment, and then radiated with 193 nm deep-UV. At this time, harmful crystals C are formed on the surface of the photomask A and the pellicle B. These crystals C lower the transmittance of the photomask A and the pellicle B, thereby resulting in distortion of the circuit pattern on mask reticle or low yielding rate. Sometimes, the whole lot of wafers becomes unusable. This problem is indeed serious. This problem is also seen in the old manufacturing process with 365 nm ultraviolet light. However, because the old manufacturing process employs a relatively longer wavelength that has a relatively lower energy to provide a relatively lower capacity, the transparency of crystals formed on wafers after radiation is still high enough, and the problem of crystal formation on wafers during running of the old manufacturing process is never so serious to obstruct the product. According to experimentation, the transmittance of crystals formed on the wafers after radiation with 365 nm ultraviolet light T=76.1%; the transmittance of crystals formed on the wafers after radiation with 248 nm deep-UV T=29.2%, which is approximately the limit; the transmittance of crystals formed on the wafers after radiation with 193 nm deep-UV T=13%, which is about the opaque status. If this problem is not settled, semiconductor manufacturing process will be limited to 0.11 μm, and the unit transistor capacity will not be doubled as within 18 months as expected subject to Moore's law.
According to Example I in FIG. 2, the photomask A and the pellicle B were kept in an enclosed plastic storage container D at 40° C. for 3 days, and then the photomask A and pellicle B were taken out of the enclosed plastic storage container D and put in a mini-environment and radiated with 193 nm deep-UV, and crystals C were found on the surface of the photomask A and the pellicle B. According to Example II in FIG. 2, the photomask A and the pellicle B were put in an enclosed plastic storage container D at 40° C. for 3 days, and then mask reticle A was taken out of the enclosed plastic storage container D and put in a mini-environment and radiated with 193 nm deep-UV, and crystals C were found on the surface of the photomask A. According to Example III in FIG. 2, the photomask A and the pellicle B were put in an enclosed stainless steel storage container D at 40° C. for 3 days, and then the photomask A and the pellicle B were taken out of the enclosed stainless steel storage container D and put in a mini-environment and radiated with 193 nm deep-UV, and no crystal formation was seen on the surface of the photomask A and the pellicle B. This study shows crystal formation has a great concern with the storage container D.
According to study, we wound the reasons of crystal formation as follows.
1. According to analysis, the chemical formula of the crystals formed on the photomask and the pellicle is (NH4)2SO4, mainly composed of (NH4)+ and (SO4)2−. During synthesis, there are important catalysts: (a) light source of short wavelength and high energy, (b) organic or inorganic gas, (c) environment humility.
2. Either the use of Krypton fluoride excimer laser to generate 248 nm deep-ultraviolet light or Argon fluoride excimer laser to generate 193 nm deep-ultraviolet light, the narrow pulse light has a high energy that is continuously supplied during photolithography, which causes crystal formation upon its radiation on photomask. It shows that the shorter the wavelength is, the higher the energy and the lower the transmittance of crystal will be.
3. Poor airtight status of the storage container allows passing of wet air (water molecule) from the outside clean room into the inside of the storage container to provide element requisite for its chemical reaction, and therefore crystals are formed on the surface of the photomask and the pellicle after removal from the storage container and radiation with 193 nm deep-UV.
4. The material of the storage container itself releases harmful gas that penetrates into the inside of the pellicle, thereby causing formation of crystals on the photomask and the pellicle after removal from the storage container and radiation with 193 nm deep-UV.
5. Because the pellicle frame is made of aluminum alloy treated with a sulfuric acid anodizing process, a big amount of sulphate ion (SO4)2− is left on the surface of the aluminum pellicle frame.
In order to prevent the aforesaid crystal formation problem, the most important measure is to enhance the airtight status of the storage container. As shown in FIGS. 3 and 4, comprises a container door (a), a packing strip (a1) covered with a layer of film material (a2) and fastened to the periphery of the container door (a). When the user closed a top cover (b) on the container door (a), a sharp edge (b1) of the top cover (b) is pressed on the layer of film material (a2) against the packing strip (a1) to seal the gap. Further, the storage container has a lifting mechanism for allowing the top cover (b) to be moved vertically between the close position and the open position. For easy opening of the top cover to meet SMIF specifications, the lifting mechanism cannot provide a relatively stronger locking force. Further, because the container door (a) is a square structure over 200 mm×200 mm and because the packing strip (a1) and the layer of film material (a2) are flexible and extended over the periphery of the container door (a), the surface of the layer of film material (a2) is not kept smooth. When closing the top cover (b) on the container door (a) to press the sharp edge (b1) of the top cover (b) on the layer of film material (a2) against the packing strip (a1) to the hard shell of the top cover (b), the layer of film material (a2) and the packing strip (a1) may receive different components of force from the top cover (b) at different locations (due to manufacturing tolerance in precision of the top cover). At this time, the small locking force of the lifting mechanism is insufficient to keep the whole area of the sharp edge (b1) of the top cover (b) engaged into the layer of film material (a2) against the packing strip (a1), and local tiny crevices (c) will be left in between the sharp edge (b1) of the top cover (b) and the layer of film material (a2), allowing outside air to pass through the local tiny crevices (c) into the inside of the storage container.
Further, the aforesaid enclosed storage container (semiconductor transferring container) generally has a valve structure through which an inertia gas can be filled into the inside space of the container. As illustrated in FIG. 6, the valve structure of the container (e) comprises a through hole (e1), a T-valve (f), which is mounted in the through hole (e1) and has an axial insertion hole (f1) and a radial outlet (f2), and a spring member (g) mounted inside the through hole (f1) around the T-valve (f) to hold the T-valve (f) in the close position. When inserting a nozzle tip (h) into the insertion hole (f1) to lift the T-valve (f) upwards from the bottom wall of the container (e), the radial outlet (f2) is opened, and an inertia gas can then be supplied through the nozzle tip (h) into the inside of the container (e). After removal of the nozzle tip (h) from the T-valve (f), the spring member (g) immediately pulls the T-valve (f) back to the close position. This design of valve structure is still not satisfactory in function because movement of the T-valve (f) in the through hole (e1) will cause the spring member (g) to rub against the peripheral wall of the through hole (e1), thereby producing particles.
In general, the aforesaid prior art enclosed transferring containers have numerous drawbacks as outlined hereinafter.
1. When closed the top cover on the container door, small crevices will be left between the top cover and the container door for allowing inside clean air (inertia gas) to pass to the outside and outside foul air to pass into the inside of the container to contaminate storage wafers/masks.
2. The plastic materials of the container will release inorganic gas, such as sulfide, thereby causing formation of crystals on the surface of storage wafers/masks.
3. When filling an inertia gas into the container through the valve structure, the spring member of the valve structure will be force to rub against the peripheral wall of the through hole, thereby producing particles to contaminate storage waters/masks.
4. The hard shell of the top cover of the container and the container door may deform slightly after a long use, lowering the airtight status of the container.
5. Because tiny crevices may be left between the top cover and the container door and outside air may pass through the tiny crevices into the inside of the container gradually, storage wafers/masks cannot be kept in the container for long, and the control person must arrange storage wafers/masks subject to the law of first in first out, complicating the management.